How is the "bars" field calculated in response to "card.wireless"?

Notecard API
1

Hi,

I am interested in how the bars field is calculated in response to card.wireless request to Notecard API. I am wondering what are the thresholds and if they are correctly set for my cellular connection using Notecard WBEXN because I get 2 different signal strengths with the same bars field value:
Response example 1: “rssir”:-91,“rssi”:-91,“rsrp”:-120,“sinr”:4,“rsrq”:-12,“bars”:1,
Response example 2: “rssir”:-63,“rssi”:-76,“rsrp”:-104,“sinr”:-20,“rsrq”:-10,“bars”:1

I found documentation about signal quality table here, does bars field match this table so the Poor row is 1 bars, Fair row is 2 bars and so on?
Does this table change depending on Network technology used (LTE Cat-1) and Notecard HW version (WBEXN)?

From other LTE signal strength tables I found online this RSSI values I am getting in the second example would be considered excellent signal quality. Is there something I am missing in this calculation?

I appreciate any insight in this, thank you.
Renato

3

Hi @Renato,

We use a proprietary algorithm in the Notecard firmware to calculate the bars metric and it’s effectively based on “worst” measure of all those values. For instance, here is the logic translated into plain english:

1. Start with 4 bars.

2. If RSRQ is unavailable:
   a. Use RSSI as the signal indicator.
   b. If RSSI < -70 dBm, reduce to 3 bars.
   c. If RSSI < -85 dBm, reduce to 2 bars.
   d. If RSSI < -100 dBm, reduce to 1 bar.
   e. Return the result.

3. If RSRQ is available:
   a. Evaluate RSRP:
      - If RSRP < -80 dBm, cap at 3 bars.
      - If RSRP < -90 dBm, cap at 2 bars.
      - If RSRP < -100 dBm, cap at 1 bar.

   b. Evaluate SINR:
      - Convert the raw SINR value into dB.
      - If SINR < 20 dB, cap at 3 bars.
      - If SINR < 13 dB, cap at 2 bars.
      - If SINR <= 0 dB, cap at 1 bar.

   c. Evaluate RSRQ:
      - If RSRQ < -10 dB, cap at 3 bars.
      - If RSRQ < -15 dB, cap at 2 bars.
      - If RSRQ < -20 dB, cap at 1 bar.

4. Return the lowest bar value produced by any of these checks.

So looking at your values, the RSRP is the issue.

Hope that helps!
Rob

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